Thermogravimetry of thermoplastic polyimide powders under four different atmospheres

Thermal degradation of a thermoplastic polyimide (TPI) fine powder was studied in nitrogen, helium, argon, and air, from room temperature to 790°C by a high-resolution thermogravimetry (TG) at a variable heating rate in response to changes in the weight-loss rate of the sample and also by traditionnal TG. In the three inert atmospheres, the high-resolution TG found a two-step degradation process with higher resolution for the TPI, which was hardly ever revealed by a traditional TG for the TPI and other similar polyimides. On the contrary, only a traditional TG in air observed a two-step degradation process for the TPI. The initial thermal degradation temperature T d' the temperatures at the maximum weight-loss rate T dm1 and T dm2' the first maximum weight-loss rate (Dα/dT) m1 , as well as the degradation activation energy of the TPI all increase with the variation of testing atmosphere in the following order : in nitrogen < in helium < in argon < in air, but the char yield at 700°C appears to increase in a different order: in air < in helium < in argon < in nitrogen.